T-square



' (No Model.)

A. HOERMANN.

T SQUARE. No. 248,652. Patented Oct. 25,1881.

WITNESSES INVENTOR WQVW BY ATTORNEY N, PETERS Pnolo-Lllimgrnplmr. \Vnshmglcm n. c.

NITED STATES PATENT OFFICE;

ARNOLD HOERMANN, OF HOBOKEN, NEW JERSEY.

T-SQUARE.

SPECIFICATION forming part of Letters Patent No. 248,652, dated October 25, 1881.

Application filed August 5, 1881.

To all whom it may concern Be it known that I, ARNOLD HOERMANN, of Hoboken, in the county of Hudson and State of New Jersey, have invented certain new and useful Improvements in T-Squares, of which the following is a specification.

The object of this invention is to furnish for offiee and school purposes an improved T- square the blade of which can be adjusted to any desired angle by a simple and reliable mechanism Without the use of a clampingscrew; and the invention consists ofaT-square the blade of .which is fitted by a conically-t-apering pivot-plate into a correspondingly-tapering recess of the head, and tightly secured in position thereon by means of a clamping lever-plate, which engages, by interior radial ribs, inclined cheeks of a plate secured to the under side of the head.

In the accompanying drawings, Figure 1 represents a plan view of my improved T- square. Fig. 2 is a vertical central section of the same on line a: 00 of Fig. l; and Figs. 3 and 4. are detail views, respectively, of the clamping lever-plate and of the bottom plate of the head of the T-square.

Similar letters of reference indicate corresponding parts. 7

Referring to the drawings, A represents the head, and B the blade, of my improved T- square. The blade B is pivoted to a central perforation of the head A by means of a pivotplate, 0, which is secured to the under side of the blade by suitable screws, rivets, or otherwise. The circumference of the pivotplate O is conically beveled and fitted into a correspondingly-beveled recess, a, of the head A. To the under side of the head A is secured a plate, D, having two or more inclined cheeks, (I, along which the interior radial ribs (1 of a clamping lever-plate, E, are moved when the same is turned on the center-pivot b of the plate 0. The lever-plate E turns loosely on the shank of the fastening-screw c, which is screwed into the pivot of the plate 0, a spiral or flat friction-spring, f, being preferably interposed between thepivot-plate G and the recess (No model.)

a of the head of the T-square for preventing any rattling, though for the cheaper kind of T-squares this spring may be dispensed with. By turning the lever-plate E in one direction the interior ribs of the same move upon the inclines of the bottom plate, D, and serve to draw the blade B into frictional contact with the conical recess of the head, so as to secure it tightly and reliably in any desired position thereon. By movingthelever-plateintheopposite direction the blade is released for adjustment on the head. In the better classes of T- squares a graduated scale may be arranged on the head, so as to set off any desired angle by means of a pointer secured to the end of the blade.

For the cheaper styles of blades, such as are used in school, I prefer to cast the pointer directly into the body of the conically-beveled pivot-plate, and use it in connection with a fixed index-point of the head for quickly setting and securing the blade at right angles to the head. By this construction a reliable adjustment of the blade to any desired angle may be accomplished, the clamping mechanism having the advantage that all parts are of cast metal and not as liable to get out of order as the clamping-screws heretofore employed.

Having thus described my invention, I claim as new and desire to secure by Letters Patent- In a T'square, the combination of a blade having a conically-beveled pivot-plate fitting into acorrespondin gl y-beveled recess or socket of the head, with a fixed bottom plate, having inclined cheeks secured to the under side of the head, and with a centrally-pivoted clampinglever-plate having interior radial ribs moving along the cheeks of the bottom plate, substantially as described.

I11 testimony that I claim the foregoing as my invention I have signed my name, in presence of two witnesses, this 1st day of August, 1881.

ARNOLD HOERMANN.

Witnesses:

PAUL GOEPEL,

CARL KARP. 

